1. Field of the Invention
The present invention relates to an image forming apparatus such as a wet type electrophotographic printer. More particularly, the present invention relates to a used developer cleaning system for cleaning used developer remaining on an image transfer medium such as an image transfer belt or a photoconductor after a developer image has been transferred, and an image forming apparatus having the same.
2. Description of the Related Art
In general, image forming apparatuses form an electrostatic latent image on a photosensitive belt or a photosensitive drum, develop the electrostatic latent image using one or more developers which each have a predetermined color, and then transfer the developed image to a recording medium such as paper. Thus, -a desired image is obtained. Electrophotographic image forming apparatuses are typically classified into wet and dry types depending on the kinds of developers used in the image forming apparatuses. For example, a wet type image forming apparatus uses liquid developer formed by mixing powdered toner with a volatile liquid carrier.
FIG. 1 shows a conventional wet type electrophotographic color printer using liquid developer.
As shown in FIG. 1, the wet type electrophotographic color printer 1 comprises an image forming unit 5, a transfer belt unit 10, a fixing unit 24, a paper-discharge unit 30, and a used developer cleaning unit 50.
The image forming unit 5 comprises four laser scanning units 11, four charge rollers 12, four photoconductors 9, and four developing devices 13 in order to form images of four colors, for example, black, yellow, cyan and magenta images.
Each developing device 13 comprises a developer reservoir 6, a developing roller 7, a deposit roller 14, a metering roller 15, and a cleaning roller 16. The developer reservoir 6 stores liquid developer 48. The developing roller 7 is positioned below a corresponding photoconductor 9. The deposit roller 14 is located below the developing roller 7 and applies an electric charge to the liquid developer 48, thereby forming an electrically charged developer film on the developing roller 7. The metering roller 15 regulates the developer film to contain a predetermined quantity of toner or concentration (% solid). Meanwhile, a predetermined level of voltage is applied to the electrically charged developer film formed on the developing roller 7 through the deposit roller 14 and supplies the electrically charged developer into a nip between the developing roller 7 and the corresponding photoconductor 9. The cleaning roller 16 cleans the developing roller 7.
The deposit roller 14 and the metering roller 15 serve to feed a developer film having a predetermined quantity of toner to the nip between the developing roller 7 and the photoconductor 9 irregardless of the concentration of liquid developer in a concentration range of about 3-40 solid %.
Each photoconductor 9 comprises a photosensitive drum and the corresponding developing device 13 forms a developer image on the photoconductor 9, the color of which is different from a developer image formed on any other photoconductor 9.
The transfer belt unit 10 comprises first transfer rollers 8, a second transfer roller 23, and an image transfer belt 17. The image transfer belt 17 is rotated along an endless track enclosing first, second and third support rollers 19, 20, 21 by a belt driving roller 22. The first transfer rollers 8 each transfer a developer image formed on a corresponding photoconductor 9 to the image transfer belt 17. The second transfer roller 23 transfers the developer image transferred to the image transfer belt 17 to a recording medium P.
The fixing unit 24 comprises first and second heating rollers 25, 27 and first and second compressing rollers 26, 28. The first and second heating rollers 25, 27 heat the developer image transferred to the recording medium P, and the first and second compressing rollers 26, 28 compress the recording medium P against the first and second heating rollers 25, 27 with a constant pressure. An image is fixed on the recording medium P by heat and pressure exerted by the first and second heating rollers 25, 27 and the first and second compressing rollers 26, 28. Then, the recording medium P is discharged out of the printer via the paper discharge unit 30 by first and second paper-discharge rollers 31, 32 and first and second paper-discharge backup rollers 33, 34.
The used developer cleaning unit 50 comprises a cleaning blade 51 for removing used developer 54 remaining on the image transfer belt 17, a used developer gutter 63 for collecting the used developer 54 removed by the cleaning blade 51, and a used developer bin 40 for storing the used developer 54 collected by the used developer gutter 63. The used developer bin 40 is typically communicated with the used developer gutter 63 via a connection tube 66.
The wet type electrophotographic color printer 1 configured as described above is operated in the following manner.
First, as a print command is issued, the image forming unit 5 operates its individual components to perform a series of image forming operations for forming an image of four colors.
Specifically, each photoconductor 9 is formed with a layer of electric charges corresponding to a color image to be printed, for example, an electrostatic image, by a corresponding charge roller 12 and a corresponding scanning unit 11. Additionally, toner of a developer film formed on a corresponding developing roller 7 from the liquid developer 48 of a corresponding reservoir 6 by a corresponding deposit roller 14 and a corresponding metering roller 15 is deposited to the area formed with the electrostatic image to form a developer image, wherein the developer film contains a predetermined quantity of toner.
At this time, the liquid developer 48 is formed as an electrically charged developer film on the developing roller 7 by an electric charge applied by the deposit roller 14 and the electrically charged developer film is transformed into a developer film containing a predetermined quantity of toner on the developing roller 7. Further, the metering roller 15 applies a predetermined level of voltage to the electrically charged developer film.
Each developer image developed on each photoconductor 9 by a corresponding developing device 13 is primarily transferred to the image transfer belt 17 from the photoconductor 9 by voltage and pressure applied and exerted by a corresponding first transfer roller 8 positioned on the inside of the image transfer belt 17. As the image transfer belt 17 is rotated along the first, second and third support rollers 19, 20, 21 by the belt driving roller 22, the developer image is transferred to the image transfer belt 17 and is moved to the second transfer roller 23. Next, the developer image is transferred to a recording medium P by the voltage and pressure applied and exerted by the second transfer roller 23.
The developer image transferred to the recording medium P is fixed to the recording medium P by the first and second heating rollers 25, 27 and the first and second compressing rollers 26, 28. Thus, a desired image is formed.
Thereafter, the recording medium P is discharged out of the paper discharge unit 30 of the printer 1 via the first and second paper-discharge rollers 31, 32 and the first and second paper-discharge backup rollers 33, 34.
After the developer image has been transferred to the recording medium P, the image transfer belt 17 continuously rotates and moves the cleaning blade 51 mounted on one side of the third support roller 21 into contact with the image forming side of the image transfer belt 17. The used developer 54 remaining on the surface of the image transfer belt 17 (typically, not 100% but 90-95% of developer is transferred to a recording medium) is removed from the image transfer belt 17 by the cleaning blade 51 for the purpose of printing a next image, collected into the used developer gutter 63, and then retrieved into the used developer bin 40.
The image transfer belt 17, from which the used developer 54 has been removed, repeats the above-mentioned operations in order to form a next image again through the individual photoconductors 9, laser scanning units 11 and developing devices 13.
The conventional printer 1, configured as described above, stores the used developer 54 removed by the cleaning blade 51 not in the used developer gutter 63 but in the used developer bin 40 which communicates with the used developer gutter 63 via the connection tube 66. Thus, leakage of the used developer 54 which causes pollution is prevented.
However, since the used developer 54 is formed from, for example, liquid containing toner sludge, a problem may arise in that the connection tube 66, which interconnects the used developer gutter 63 and the used developer bin 40, may clog due to the sludge if the used developer 54 collected in the used developer gutter 63 by the cleaning blade 51 is sent to the used developer bin 40 without being filtered.
If the connection tube 66 were clogged, the used developer 54 is continuously collected in the used developer gutter 63. Consequently, the used developer 54 may overflow from the used developer gutter 63 or leak out when the image forming unit 5 or the like is replaced. If the used developer 54 overflows or leaks from the used developer gutter 63, a problem will arise in that the peripheral components such as the transfer belt unit 10 or the like is contaminated. This may reduce the life span of such components.
In order to address these problems, the conventional printer 1 is provided with a sludge filtering screen 65 within the used developer gutter 63 as shown in FIG. 2.
The sludge filtering screen 65 is formed from a grid like metallic or plastic mesh. The sludge filtering screen 65 separates the used developer 54 collected in the used developer gutter 63 by the cleaning blade 51 into for example, particulate sludge and sends only, for example, Norpar/carrier liquid to the used developer bin 40 through the connection tube 66. The particulate sludge filtered by the sludge filtering screen 65 remains in the used developer gutter 63 until the image forming unit 5 serves its time, and the filtered and collected sludge will be disposed along with the image forming unit 5 when the image forming unit 5 is disposed.
However, because such a sludge filtering screen 65 can filter only the sludge having a grain size larger than the mesh of the screen, there is a problem in that particulate sludge having a grain size smaller than the mesh of the screen passes through the sludge filtering screen 65. Accordingly, a problem may still arise in that the small grains of sludge passing through the sludge filtering screen 65 may still render the connection tube 66 clogged.
In addition, there is a problem in that because the sludge filtering screen 65 should be adapted to the shape of the used developer gutter 63, the sludge filtering screen 65 is difficult to mass produce. In addition, because a mold is additionally needed when fabricating such a sludge filtering screen 65, the manufacturing costs thereof are high.
Therefore, what is needed is to provide a used developer cleaning system having a sludge filtering device which can effectively remove sludge contained in used developer 54 and which can be easily fabricated without expending high manufacturing costs.
Accordingly, there is a need for an improved image forming apparatus having a used developer cleaning system with a sludge filtering device which can effectively remove sludge contained in the used developer which can be easily fabricated without expending high manufacturing costs.